The KN52 antibody reacts with human integrin beta 5, an approximately 100,000 Mr (reduced) and 95,000 Mr (nonreduced) a member of the integrin family. Only a single alpha chain, the alpha v subunit, associates with the integrin beta 5 to form the vitronectin receptor complex. Integrin alpha v/beta 5 complex also binds to the basic domain of Tat (he sequence RKKRRQRRR). The integrin beta 5 is found on carcinoma cell lines, hepatoma and fibroblast cell lines, and is absent from lymphoblastoid cells and platelets.